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HVAC Chiller Maintenance Tips

HVAC Chiller Maintenance Tips To Improve AC System Efficiency

The efficiency of your HVAC chiller system is an important consideration when it comes to keeping your cool. With high energy costs, modern air conditioning systems are designed to run as efficiently as possible. However, a properly sized and installed chiller can increase the efficiency of your system and lower your energy bills. This guide will explain how your chiller works, measures you can take to increase its efficiency. 

3 Ways To Increase HVAC Chiller Efficiency

1. Consider variable speed reuse

Variable speed drives can benefit most components in a chilled water system. In fact, current performance codes typically require Variable Frequency Drives for these components on new systems and major retrofits. The cost of VFDs has also fallen dramatically in recent years.

As shown in the efficiency charts for fixed and variable speed air conditioning on page 38, VFDs are dependent on condenser water temperature relief being implemented. Variable Frequency Drives are another way to save energy with another way to save energy. When outdoor wet-bulb and load temperatures drop, variable-speed fan motors not only save fan energy due to fan law benefits (a fan running at 50 percent speed consumes 12.5 percent of the energy of a fan running at full speed), but also provide for a more stable temperature.

The variable speed pump may present an opportunity to save energy, but it would require a close look at other parts of the system. On the cold water side, a change from constant to variable flow can entail significant and expensive upgrades to control valves and control sequences. In addition, the variable flow rate options of existing coolers must be examined. Limited chilled water flow limits can reduce the return on investment for variable chilled water pumping. On the condenser water side, variable flow control is limited by cooling tower icing/plating issues or HVAC chiller liquid requirements. However, if the pumps in a constant flow system are oversized, balancing the flow of the pump by slowing it down or limiting the flow by an offset value can provide good recovery even without adding variable flow to the system during operation.

2. Running multiple parallel devices improves storage

Refrigeration systems generally work optimally at part loads.For example, chillers can operate most efficiently at between 40 and 60 percent of full load. Cooling tower fans and pump systems connected in parallel can be used to improve performance by running more units at lower speeds than a staging scheme, which allows each unit to run at its full capacity before the next unit is installed. For cooling towers and chillers, Ran Optimized Heat Transfer maximizes the heat transfer area at all operating points, optimizing energy efficiency and reducing pressure drops. It is crucial for water pumps to take advantage of the savings from the Energy Policy Act and work at most efficient points. (The law of the pump is the law of the fan: if the speed of the pump is reduced, the energy efficiency increases by the cube of the speed reduction). Any changes to the control scheme must take into account the minimum flow limits of the cooling tower and cooling system.

3. Increasing the supply temperature of HVAC chiller

Most commercial systems are designed with a chilled water supply temperature in the 40 to 45 degrees Fahrenheit range. This generally allows adequate dehumidification and acceptable supply air temperatures for the habitable spaces during peak periods. Nevertheless, these are rare conditions which are rarely encountered. There are several ways to reduce energy consumption by applying reset control of the supply air temperature. First, when cold air supply temperature requirements are not needed (acceptable levels of humidity, and no peak load zones), increasing supply temperatures can help to prevent excessive dehumidification of spaces and unnecessary latent cooling. More importantly, increasing the supply air temperature has the effect of raising the chilled water feed temperature, achieving a significant improvement in chiller efficiency. It is expected that the efficiency of HVAC chillers would improve by approximately 2 percent for each degree that their chilled water supply temperature rises.  

Any design and control features that should be analyzed to save energy should also be considered. As mentioned above, VFDs should be considered in all or some components of an energy-harvesting device. Furthermore, a close look at setpoints, temperature resets, and other simple control sequence changes is often effective at minimal cost. Although this method is not appropriate for all systems. There is no doubt that depending on the budget and financial requirements, climate, expected load profile, and existing device constraints, the optimal solutions will vary and will require engineering analysis and annual energy consumption calculations.

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